With reference to FIG. 1, a ducted fan gas turbine engine generally indicated at 10 has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, and intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.
The gas turbine engine 10 works in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 14 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.
The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.
Each blade of the fan 12 is mounted on a rotor disc by inserting a root portion of the blade in a complementary retention groove in the outer face of the disc periphery. To ensure a smooth radially inner surface for air to flow over as it passes through the stage, annulus fillers can be used to bridge the spaces between adjacent blades. Typically, a seal between the annulus fillers and the adjacent fan blades is also provided by resilient strips bonded to the annulus fillers adjacent the fan blades. The fillers may be manufactured from relatively lightweight materials and, in the event of damage, may be replaced independently of the blades.
It is known to provide annulus fillers with features for removably attaching them to the rotor disc. An annulus filler may be provided with axially spaced hook members, the hook members sliding into engagement with respective parts of the rotor disc and/or a component located axially behind the rotor assembly, for example a rear fan air seal. FIG. 2 shows an example of such an annulus filler 32 viewed from the rear.
In use, the upper surface or lid 34 of the annulus filler 32 bridges the gap between two adjacent fan blades (not shown) and defines the inner wall of the flow annulus of a fan stage. The annulus filler 32 is mounted on a fan disc (not shown) by two hook members 36 and 38, respectively towards the forward and rearward ends of the annulus filler 32. It is also attached to a support ring (not shown) by a mounting feature 40. The two opposed side faces 42, 44 of the annulus filler are provided with respective seal strips 46, 48, and confront the aerofoil surfaces of the adjacent fan blades. Typically the annulus filler is a machined aluminium alloy forging.
In the event of a flan blade off (FBO) or foreign object impact (such as bird or ice impact), it is desirable for the annulus filler to absorb impact energy in such a way that the risk of loss or damage to the filler can be reduced.